TNB Research (TNBR) required a comprehensive assessment to address the issues relating to sedimentation of Ringlet Reservoir in the Cameron Highlands for the development of an optimum sediment management strategy. Current sediment management practices are not efficient in managing the influx of sediment loads into the reservoir due to the land clearing activities further upstream. The Cameron Highlands is synonymous with fresh agricultural produce, which is highly sought after by local and overseas markets. The rapid development and land clearing have significantly altered the land cover of the Cameron Highlands, which leads to an increase in the sediment loads to the reservoir. The sediment-laden flows have resulted in greatly reduced storage capacity and consequently led to reduced power generation and flood control, with potential negative impacts on the safety of the dam.

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Challenge

The challenge of managing reservoir sedimentation

Ringlet Reservoir forms part of the Cameron Highlands Batang Padang hydroelectric scheme that was completed more than 50 years ago. The reservoir is formed by the Sultan Abu Bakar dam, constructed in 1963. Since then, land clearing activities for agricultural and urbanised areas in the upper catchments have mobilised millions of tons of additional sediment into the reservoir. This regrettably accelerated the sedimentation of the reservoir, resulting in a loss of operational volume for hydropower generation. The incoming sediment to the reservoir is estimated to be in the region of 300,000 m3/year, which is about 10 times that of the design sedimentation rate.

TNB has constructed two sediment check dams at the main inlets (Habu and Ringlet ends) to reduce the sediment inflows and maintain the storage capacity of the reservoir. The retained sediments are continuously removed from the check dams while dredging is carried out in the reservoir itself. To better manage these sediments, a robust and sustainable sediment management plan is required to be drafted and implemented. Thus, an extensive study has been carried out to quantify the complex morphological changes in the reservoir and evaluate the effectiveness of a range of sediment management practices.

Reservoir sedimentation has resulted in a loss of operational volume for hydropower generation. © DHI

Solution

At DHI, we have experience in hydrodynamics and morphological modelling of reservoirs and the impact of sedimentation on the service life of these reservoirs. Our dedicated MIKE 21 Hydrodynamics Flow Model (HD FM), complemented by the MIKE 21 Mud Transport (MT) module allows for the prediction of sedimentation rates within the reservoir and the annual maintenance dredging required. With MIKE 21 MT, we can simulate the change in bed thickness of the main reservoir, along with the volume of sediments accumulated behind check dams.

The numerical modelling of the reservoir serves as the primary tool to assess the current sedimentation issues and to investigate various mitigation solutions. These, in turn, require substantial amounts of data and to be supported by a dedicated site survey campaign. Given the rapid pace of development in the catchment, the hydrodynamic and sediment transport models are challenging to calibrate. The sediment input into the model is supplemented by DHI’s in-house equipment SediScat Pro, which proved to be successful in estimating the particle size distributions at various locations within the tributaries and the reservoir body.

Besides appraising the impact of land clearing on the sedimentation rates, we have also provided the following services:

  • Evaluation of current best practices in reservoir sediment management
  • Review of the current dredging and desilting operations
  • Numerical modelling to provide a platform to assess the current sediment loading and test the practicality of various mitigation and management options
  • Development of a sustainable sediment management plan for Ringlet Reservoir

In total, eight different mitigation options were developed based on improving the retention performance in the upper parts of the reservoirs, increasing the reservoir flushing and introducing sediment bypass tunnel. The improvement in sediment management oversees a reduction of reservoir deposition of between 14% and 54% over the baseline conditions. The established sediment management strategies ensure that the long-term resilience of this critical infrastructure facility is safeguarded.

Ringlet Reservoir model with artificial dykes (Left – model setup, Middle – current speed, Right – Total Suspended Solids Concentration). © DHI

Results

Ability to test a range of
reservoir sedimentation
management practices

More robust and efficient decision-making driven by numerical modelling

Easier access to validated data for making risk-based and infrastructure-specific decisions

About the client

TNB Research Sdn. Bhd (TNBR) is the research arm of a large power utility company Tenaga Nasional Berhad (TNB) in Malaysia. Its mission is to enhance Stakeholders Interest through its commitment to pioneer and develop technical solutions and innovation under various Applied Research projects. These solutions have contributed towards improving the overall operational performance.

Software used

MIKE HYDRO River
MIKE 21 Hydrodynamics (HD)
MIKE 21 Mud Transport (MT)

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Extending the life of a hydropower plant

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